Retinoic acid enhances the initiation of DNA synthesis stimulated by prostaglandin F in Swiss 3T3 cells

Retinoic acid at concentrations of 10−8–10−6M increases the initiation of DNA synthesis stimulated by prostaglandin F2α (PGF2α), alone or with insulin, in confluent resting Swiss mouse 3T3 cells. Analogues of retinoic acid had a similar effect. Adding retinoic acid, alone or with insulin, did not stimulate DNA synthesis. The synergistic effect of PGE1 or PGE2 with PGF2α and insulin was not further enhanced by retinoic acid. Neither the synergistic effect of retinoic acid nor that of PGE1 or PGE2 with PGF2α was affected by indomethacin, an inhibitor of prostaglandin synthesis. The results suggest that the synergy of retinoic acid with PGF2α is not mediated through an increase of prostaglandin synthesis and that retinoic acid stimulates event(s) in common with those of PGE1 and PGE2 leading to an increase in the initiation of DNA synthesis.